Introduction to Computing Principles - - PowerPoint PPT Presentation

天津大学 计算机科学与技术学院 刘志磊

Introduction to Computing Principles

计算原理导论

Data

Data is a set of values of qualitative or quantitative variables.

• - Wikipedia

Introduction to Computing Principles Structured Data

Data Table Code

Structured data refers to any data that resides in a fixed field within a record

• r file. This includes data contained in relational databases and spreadsheets.

Table

A table is a means of arranging data in rows and columns. The use of tables is pervasive throughout all communication, research, and data analysis. A table consists of an ordered arrangement of rows and columns.

• - Wikipedia

Introduction to Computing Principles Structured Data

Data Table Code

Table Example - Social Security Baby Name

On the Social Security Baby Name site:

• Names for babies born each year in the USA
• Top 1000 boy and girl names, 2000 names total

Introduction to Computing Principles Structured Data

Data Table Code

Table Example - Social Security Baby Name

• Table terminology (术语):
• table the whole rectangle of data
• row data for one name
• field individual items (columns) in a row
• Each field has a name: name, rank, gender, year

Introduction to Computing Principles Structured Data

Data Table Field

Tables Are Extremely Common

• Rectangular table format is very common
• Database: extension of this basic table idea
• Number of fields is small (categories)
• Number of rows can be millions or billions

Examples

• email inbox
• one row is one message
• fields: date, subject, from, ...
• craigslist
• one row is one thing for sale
• fields: description, price, seller, date, ...

Introduction to Computing Principles Structured Data

Data Table Field

Code and Practice - SimpleTable

• Baby data stored in "baby-2010.csv"
• ".csv" stands for "comma separated values“
• csv is a simple and widely used standard format to store a table as text in a file.
• For images: for(pixel: image) { code }
• For tables: for (row: table) { code }
• For print: print(row)
• prints out the fields of a row on one line

Introduction to Computing Principles Structured Data

Code For-loop If-statement

For-loop

table = new SimpleTable("baby-2010.csv"); for (row: table) { print(row); }

Introduction to Computing Principles Structured Data

Code For-loop If-statement

Example

If-statement

• For select: if-statement
• if ( condition ) { code }
• Terminology: “query” (查询)
• for: runs for every row (2000 rows)
• if: picks out some

Introduction to Computing Principles Structured Data

Code For-loop If-statement

If-statement

table = new SimpleTable("baby-2010.csv"); for (row: table) { if (row.getField("rank") == 6) { print(row); } }

Introduction to Computing Principles Structured Data

Code For-loop If-statement

Example

Query Logic

• Field names for the baby table: name, rank, gender, year
• Pick field out of row: getField
• row.getField(“field-name”)
• two equal signs and single equal sign
• =

: variable assignment

• == : variable comparison
• use == inside if-test
• Other comparisons

< > <= >=

Introduction to Computing Principles Structured Data

Query Logic startsWith & endsWith Boolean Logic

Query Logic

table = new SimpleTable("baby-2010.csv"); for (row: table) { if (row.getField("name") == "Alice") { print(row); } }

Introduction to Computing Principles Structured Data

Query Logic startsWith & endsWith Boolean Logic

Query Logic

• Baby table fields: name, rank, gender, year
• name field is "Robert", "Bob", "Abby", "Abigail" (try each in turn)
• rank field is 1
• rank field is < 10
• rank field is <= 10
• rank field is > 990
• gender field is "girl"
• rank field is less than 15
• gender field is "boy"

Introduction to Computing Principles Structured Data

Query Logic startsWith & endsWith Boolean Logic

Query Logic

table = new SimpleTable("baby-2010.csv"); for (row: table) { if (row.getField("name") == "Alice") { print(row); } } // Change string to "Robert", "Bob", etc. if (row.getField("rank") == 1){ print(row); } if (row.getField("rank") < 10){ print(row); } if (row.getField("rank") <= 10){ print(row); } if (row.getField("rank") > 990){ print(row); } if (row.getField("rank") < 15){ print(row); } if (row.getField("gender") == "girl"){ print(row); } if (row.getField("gender") == “boy"){ print(row); }

Introduction to Computing Principles Structured Data

Query Logic startsWith & endsWith Boolean Logic

startsWith & endsWith

• == : very handy for baby names
• Test if the name field in a row starts with "Ab":
• if (row.getField("name").startsWith("Ab")) { ...
• Test if the name field in a row ends with "zy":
• if (row.getField("name").endsWith("zy")) { ...

Introduction to Computing Principles Structured Data

Query Logic startsWith & endsWith Boolean Logic

startsWith & endsWith

table = new SimpleTable("baby-2010.csv"); for (row: table) { if (row.getField("name").startsWith("Ab")) { print(row); } }

Introduction to Computing Principles Structured Data

Query Logic startsWith & endsWith Boolean Logic

Example

startsWith & endsWith

if (row.getField("name").startsWith("Ab")) { print(row); } // Change string to "A", "a", "Z", .. each in turn name field starts with "Ab", "A", "a"(lower case) name field starts with "Z", "Za" (each in turn) name field ends with "z", "ly", "la" (each in turn) if (row.getField("name").endsWith("z")) { print(row); }// Change string to “z", “ly", “la", .. each in turn

Introduction to Computing Principles Structured Data

Query Logic startsWith & endsWith Boolean Logic

Boolean Logic (布尔逻辑)

In mathematics and mathematical logic, boolean logic is the branch of algebra (代数) in which the values of the variables are the truth values true and false, usually denoted 1 and 0

• respectively. Instead of elementary algebra where the values of

the variables are numbers, and the main operations are addition and multiplication, the main operations of Boolean algebra are the conjunction and denoted as ∧, the disjunction or denoted as ∨, and the negation not denoted as ¬. It is thus a formalism for describing logical relations in the same way that ordinary algebra describes numeric relations.

Introduction to Computing Principles Structured Data

Query Logic startsWith & endsWith Boolean Logic

Boolean Logic

• Boolean Logic: && || !
• In English, combine tests like this:
• Name starts with "A" and ends with "y"
• In code, combine tests use "boolean logic“:
• and is && (two ampersands)
• or is || (two vertical bars)
• not is !

(exclamation mark)

Introduction to Computing Principles Structured Data

Query Logic startsWith & endsWith Boolean Logic

table = new SimpleTable("baby-2010.csv"); for (row: table) { if (row.getField("name").startsWith("A") && row.getField("name").endsWith("y")) { print(row); } }

Introduction to Computing Principles Structured Data

Boolean Logic

Query Logic startsWith & endsWith Boolean Logic

• The && joins a startsWith test and an endsWith test
• The whole test is written across two lines because it is kind of long (optional)
• Standalone rule:
• the tests are syntactically complete tests on their own, then joined with && or ||
• row.getField("name).startsWith("A") && endsWith("y") Incorrect, not Standalone
• Common error
• too few right parenthesis around the test
• Run tries to detect certain common errors
• omitting the {, or typing & instead of && will give an error message

Introduction to Computing Principles Structured Data

Boolean Logic - && ||

Query Logic startsWith & endsWith Boolean Logic

table = new SimpleTable("baby-2010.csv"); for (row: table) { if (row.getField("name").startsWith("A") && row.getField("rank") <= 50) { print(row); } }

Introduction to Computing Principles Structured Data

Boolean Logic - && ||

Query Logic startsWith & endsWith Boolean Logic

table = new SimpleTable("baby-2010.csv"); for (row: table) { // your code here if (row.getField("name").startsWith("X") || row.getField("name").startsWith("Y") || row.getField("name").startsWith("Z")) { print(row); } }

Introduction to Computing Principles Structured Data

Boolean Logic - && ||

Query Logic startsWith & endsWith Boolean Logic

• name starts with "Ab" or name starts with "Ac"
• name starts with "Ab" or name starts with "Ac" or name starts with "Al"
• name starts with "O" and name ends with "a"
• name starts with "O" and gender is "girl"
• name ends with "a" and gender is "boy"
• rank is <= 10 and gender is "girl" ("top 10 girl names")
• rank is <= 10 or gender is "girl"
• name ends with "ia" and gender is "boy" (also try with gender is "girl")
• name ends with "io" and gender is "girl" (then try "boy")
• name ends with "o" and gender is boy and rank is >= 900

Introduction to Computing Principles Structured Data

Boolean Logic - && ||

Query Logic startsWith & endsWith Boolean Logic

table = new SimpleTable("baby-2010.csv"); for (row: table) { if (row.getField("name").startsWith("Ab") || row.getField("name").startsWith("Ac")) { print(row); } } if (row.getField("name").startsWith("Ab") || row.getField("name").startsWith("Ac") || row.getField("name").startsWith("Al")) { print(row); } if (row.getField("name").startsWith(“O") || row.getField("name").endsWith("A")) { print(row); }if (row.getField("name").startsWith(“O") || row.getField(“gender") == “girl”) { print(row); } if (row.getField(“rank") <= 10 && row.getField(“gender") == “girl”) { print(row); } if (row.getField("name").endsWith("a") && row.getField("gender") == "boy") { print(row); } if (row.getField(“rank") <= 10 || row.getField(“gender") == “girl”) { print(row); }

if (row.getField("name").endsWith("ia") && row.getField("gender") == "boy") { print(row); } if (row.getField("name").endsWith("io") && row.getField("gender") == "girl") { print(row); } if (row.getField("name").endsWith("o") && row.getField("gender") == "boy" && row.getField("rank") >= 900) { print(row); }

Introduction to Computing Principles Structured Data

Boolean Logic - && ||

Query Logic startsWith & endsWith Boolean Logic

• “not” operation: !
• The boolean "not" operation inverts true and false
• Two forms of not:
• ! (exclamation mark) can go in front of an s.startsWith() s.endsWith()

expression

• !row.getField("name").startsWith("A")
• names not starting with "A“, starting with any letter other than "A"
• ! = variant of = =, meaning "not equal to“
• row.getField("name") != "Alice“
• names which are not equal to "Alice“, any name other than "Alice“

Introduction to Computing Principles Structured Data

Boolean Logic - !

Query Logic startsWith & endsWith Boolean Logic

table = new SimpleTable("baby-2010.csv"); for (row: table) { if (!row.getField("name").startsWith("A")) { print(row); } }

Introduction to Computing Principles Structured Data

Boolean Logic - !

Query Logic startsWith & endsWith Boolean Logic

• girl names starting with "A" (no "nots" in this one)
• girl names not starting with "A"
• names starting with "A" and not ending with "y"
• names starting with "A" and ending with "y" and not equal to "Abbey"

Introduction to Computing Principles Structured Data

Boolean Logic - !

Query Logic startsWith & endsWith Boolean Logic

table = new SimpleTable("baby-2010.csv"); for (row: table) { if (row.getField("name").startsWith("A") && row.getField("gender") == "girl") { print(row); } } if (!row.getField("name").startsWith("A") && row.getField("gender") == "girl") { print(row); } if (row.getField("name").startsWith("A") && row.getField("name").endsWith("y") && row.getField("name") != "Abbey") { print(row); } if (row.getField("name").startsWith("A") && !row.getField("name").endsWith("y")) { print(row); }

Introduction to Computing Principles Structured Data

Boolean Logic - !

Query Logic startsWith & endsWith Boolean Logic

Inside/Outside Loop

• Loop: power technique to do something a zillion times
• Inside vs. outside the loop is a huge difference.

Experiment:

• 2000 names (rows) total, 12 names end with "x"
• We have the line: print("nom"); and we'll move it around

Introduction to Computing Principles Structured Data

Inside / Outside Loop

table = new SimpleTable("baby-2010.csv"); // Location 1 print("nom"); for (row: table) { // Location 2 if (row.getField("name").endsWith("x")) { print(row); // Location 3 } } // Location 4

Introduction to Computing Principles Structured Data

Inside/Outside Loop

Inside / Outside Loop

table = new SimpleTable("baby-2010.csv"); // Location 1 for (row: table) { print("nom"); // Location 2 if (row.getField("name").endsWith("x")) { print(row); // Location 3 } } // Location 4 Location 1: 1 (outside the loop, before it) Location 2: 2000 (in the loop, not in the if-body) Location 3: 12 (in the if-body) Location 4: 1 (outside the loop, after it)

Count

How to Count: three things to do counting 1. Create a count variable and set it to 0 before the loop

• count = 0;

2. Inside the if-statement, increase count by 1

• count = count + 1;

3. Print the final value stored in count after the loop

• print("count:", count);

Pattern: init, increment, print x = x + 1; increments the value stored in a variable

Introduction to Computing Principles Structured Data

Count

table = new SimpleTable("baby-2010.csv"); count = 0; for (row: table) { if (row.getField("name").startsWith("A")) { print(row); // Could comment this line out count = count + 1; // increases the value in count by 1 } } print("count:", count);

Introduction to Computing Principles Structured Data

Count

Count

• Try commenting out or removing the print(row); line inside the { .. } then-
• code. What is the output now?
• How many names start with "X"? Then change to count starting with "Y"?
• How many girl names begin with "A"? Then change to count how many

boy names begin with "A"?

Introduction to Computing Principles Structured Data

Count

Count

table = new SimpleTable("baby-2010.csv"); count = 0; for (row: table) { if (row.getField("name").startsWith("A")) { count = count + 1; // increases the value in count by 1 } } print("count:", count); if (row.getField("name").startsWith("X")) { count = count + 1; } if (row.getField("name").startsWith("A") && row.getField("gender") == "girl") { count = count + 1; }

Introduction to Computing Principles Structured Data

Count

Count

How to Count Multiple Things: Counting multiple things in the loop

• 1. Have multiple counters:
• count1 = 0; // boy counter
• count2 = 0; // girl counter
• 2. Series of if-statements inside the loop
• count1 = count1 + 1;
• count2 = count2 + 1;
• if-statements are not nested (more complex)
• 3. After the loop, print both counters
• print(“count1”, count1);
• print(“count2”, count2);

More mnemonic variable names, like countBoy and countGirl

Introduction to Computing Principles Structured Data

Count

Count

table = new SimpleTable("baby-2010.csv"); count1 = 0; // boy counter count2 = 0; // girl counter for (row: table) { if (row.getField("name").endsWith("y") && row.getField("gender") == "boy") { count1 = count1 + 1; } if (row.getField("name").endsWith("y") && row.getField("gender") == "girl") { count2 = count2 + 1; } } print("boy count:", count1); print("girl count:", count2);

Introduction to Computing Principles Structured Data

Count

Count

table = new SimpleTable("baby-2010.csv"); count1 = 0; count2 = 0; count3 = 0; for (row: table) { if (row.getField("name").endsWith("a")) { count1 = count1 + 1; } if (row.getField("name").endsWith("i")) { count2 = count2 + 1; } if (row.getField("name").endsWith("o")) { count3 = count3 + 1; } } print("a count:", count1); print("i count:", count2); print("o count:", count3);

Introduction to Computing Principles Structured Data

Count

Count

Spreadsheet

A spreadsheet is an interactive computer application for

• rganization, analysis and storage of data intabular form.

Spreadsheets are developed as computerized simulations of paper accounting worksheets. The program operates on data entered in cells of a table. Each cell may contain either numeric or text data, or the results of formulas that automatically calculate and display a value based on the contents of other cells. A spreadsheet or worksheet may also refer to one such electronic document.

Introduction to Computing Principles Structured Data

Spreadsheet

Spreadsheet

• A “spreadsheet” is an easy way to do simple computations
• Everyone should be able to make a basic spreadsheet
• Numbers and formulas on paper is a paradigm
• Numbers and variables in computer code is a paradigm, like x = x + 1
• Spreadsheet paradigm is rows and columns of numbers (visual)
• Spreadsheets enable math without programming, a great invention
• History: Visicalc, then Lotus, then Excel
• Spreadsheets energized the “personal computer” revolution

Introduction to Computing Principles Structured Data

Spreadsheet

Spreadsheet

• The creators of the spreadsheet knew finance math and paper spreadsheets, and they

had some computer knowledge

• Theory: knowing the problem domain creates great software more than knowing CS
• What problem to solve
• How users look at the problem
• The user's priorities
• Hidden agenda: everyone should know a little CS

Who Makes Great Software

Introduction to Computing Principles Structured Data

Spreadsheet

Spreadsheet - Cells and Naming

• A spreadsheet is a rectangle of individual cells
• Each cell can contain number, date, text, .. whatever
• Addressing: columns are named: A, B, C, D, ...
• Addressing: rows are numbered: 1, 2, 3, 4, 5, ...
• So one cell can be identified like: B3, C12, A1, ..

Introduction to Computing Principles Structured Data

Spreadsheet

Spreadsheet - sum( )

• Compute the total number of monsters in the blue castle
• Click on the B8 cell, a couple rows below the last blue castle number
• Type in the following "formula" (with the equal sign): =sum(B1:B6)
• The equal sign = at the start means this cell is computed from other cells
• The sum() adds up all the numbers in a range of cells
• The B1:B6 means the whole vertical group of cells from B1 down

through B6 (lowercase letters like b1:b6 work too)

• Type in "Total Count" in the cell to the left (A8) to serve as a label
• Famous Reinhart/Rogoff bug - wrong cells in formula

How to add a range of cells

Introduction to Computing Principles Structured Data

Spreadsheet

Spreadsheet - sum( )

• When you change a number up above, the sum is automatically updated
• Once you type in the =sum(...) in the cell, it is replaced with the computed

sum number (28 in this case)

• Click the cell, edit up above
• Double click the cell to edit
• Color shows cell-dependency
• Type in "b1:b6" vs. click-drag
• Hit the esc key to cancel out of editing, a life saver
• Using =sum() to add up a bunch of numbers is super common

Introduction to Computing Principles Structured Data

Spreadsheet

Spreadsheet - + - * /

• Suppose every monster pays $100 per night and we want to compute the $

income per night, i.e. count*100

• We can write an arithmetic formula like =B1*B2 in a cell to compute a

number based on the values of other cells

• Click the B9 cell just below the sum
• Type in the formula (with the equal sign): =B8*100
• Probably the easiest way to edit an existing formula such as in B8 and B9 is

double clicking the cell

• Trick: while typing in the formula, instead of typing "B8", just click the cell

you mean

• Type in "Total $/night" as a label to the left
• This is similar to the earlier sum() computation, but with basic + - * / type

arithmetic

Introduction to Computing Principles Structured Data

Spreadsheet

Spreadsheet - average( )

• Above sum(a1:a10) computes the total sum of range of of numbers
• Similarly, average(a1:a10) compute the average of range of numbers
• sum() and average() are probably the two most commonly used functions

Introduction to Computing Principles Structured Data

Spreadsheet

Spreadsheet - Chart

• Click on A1 (the upper left of the data) and drag down to the lower

right of the data (C6)

• Don't include the totals, just the raw numbers at the top
• Select Insert Chart
• There are many types of chart available
• Experiment with bar vs. line chart, or maybe add a title, resize it a bit
• Position the chart below all the numbers
• Notice: changing a number updates the chart
• Making pretty charts with your data is pretty easy

Introduction to Computing Principles Structured Data

Spreadsheet

Spreadsheet - Chart

Introduction to Computing Principles Structured Data

Spreadsheet

Thank You! Q&A